Metro-cluster based on synchronous replication of virtualized storage processors

ABSTRACT

A technique for managing failover from a first data storage system to a second data storage system includes configuring replication settings for data objects associated with VSPs (Virtualized Storage Processors) on a per-VSP basis, such that all of the data objects associated with each VSP share common replication settings. As the first data storage system operates a VSP, operations replicate data written to any of the data objects of the VSP to the second data storage system such that the second data storage system acquires and stores a replica of the VSP. In the event of a failure at the first data storage system, operations fail over the entire VSP, including all of its data objects, to the second data storage system, to restore host access to the data objects from the VSP replicas. A metro-cluster may be formed from multiple data storage systems that use this failover approach.

BACKGROUND

Data storage systems commonly employ replication solutions for protecting the data they store. Conventional replication solutions furnish either block-based solutions, e.g., for replicating LUNs (Logical Unit Numbers—although the term generally refers to the units themselves) or file-based solutions, e.g., for replicating file systems or individual files. Block-based solutions operate on storage volumes, e.g., using Fibre Channel or iSCSI (Internet Small Computer System Interface) protocols, whereas file-based solutions operate on files and file systems, e.g., using NFS (Network File System), CIFS (Common Internet File System), or SMB 3.0 (Server Message Block) protocols.

A well-known example of a block-based replication solution is the RecoverPoint system available from EMC Corporation of Hopkinton, Mass. RecoverPoint systems include a replication splitter realized in software, e.g., on a storage processor (SP) that accesses a local block-based array, one or more local replication appliances, and one or more remote replication appliances connected to a remote array configured as a replica site. As a data storage system receives IO requests specifying data to be written to a particular LUN on the local block-based array, the replication splitter intercepts the IO request and sends it to the local replication appliance (or appliances), e.g., over a Fibre Channel or iSCSI connection. The local appliance communicates with the remote appliance, e.g., over a WAN (Wide Area Network), and manages the storage of the data specified in the IO request at the replica site. In this manner, the replica site is made to store data that provide a redundant copy of data on the LUN, which may be used to recover the contents of the LUN in the event of a failure on the local array.

A well-known example of a file-based replication solution is the Celerra Replicator™ V2, also available from EMC Corporation of Hopkinton, Mass. Replicator V2 includes software for performing replication on files and file systems. Replicator V2 operates by taking snaps (e.g., point in time copies, also known as “snapshots” or “checkpoints”) of files and file systems at a local site, comparing current snaps with previous snaps, identifying differences, and sending the differences to a destination site. The destination site accumulates and stores the differences, which can be reconstituted to recover the file or file system being replicated in the event of a failure at the local site. File-based replication solutions often provide advanced features for establishing and maintaining replication sessions, managing recovery and failover, and ensuring that particular settings and restrictions applied to file systems being replicated carry over to replicas at the destination site.

Conventional replication solutions may perform synchronous replication or asynchronous replication. “Synchronous” replication refers to replication that takes place in band with IO requests as the IO requests arrive. With synchronous replication, data conveyed in individual IO requests are generally persisted to a replica site on an individual basis, e.g., one-by-one, as the IO requests are processed. In contrast, “asynchronous” replication is performed out of band with individual IO requests, with replicas generated, for example, on demand, at regular intervals, and/or in response to particular events. Bearing this distinction in mind, RecoverPoint may be regarded as a synchronous replication solution, although it may also provide asynchronous capabilities. Replicator V2 may be regarded as an asynchronous solution, as acquiring snaps and computing differences between them are performed out of band with IO processing.

SUMMARY

Efforts are underway to develop VSPs (Virtualized Storage Processors), i.e., groupings of data objects (e.g., file systems, LUNs, block-based vVOLs, file-based vVOLs, etc.), servers, and interfaces, which may be operated on physical storage processors (SPs) and which interact with hosts in a manner similar to the way physical SPs interact with hosts. Users can communicate with VSPs over a network to access the VSPs' respective data objects.

Each VSP may be associated with tens or even hundreds of data objects. Using conventional approaches, processes for configuring and managing failover for the data objects of a VSP have required administrators to configure failover settings on each data object individually. Given the large number of data objects that may be associated with a VSP, however, configuring and managing failover for all data objects of the VSP can place a great burden on administrators.

In contrast with the conventional approach, an improved technique for managing failover from a first data storage system to a second data storage system includes configuring replication settings for data objects associated with VSPs on a per-VSP basis, such that all of the data objects associated with each VSP share common replication settings. As the first data storage system operates a VSP, replication operations on the first data storage system replicate data written to any of the data objects of the VSP to the second data storage system, in accordance with the VSP-specific replication settings for the VSP, such that the second data storage system acquires and stores a passive replica of the VSP. In the event of a failure at the first data storage system, operations fail over the entire VSP, including all of its data objects, to the second data storage system, and activate the passive replica of the VSP at the second data storage system to restore host access to the data objects of the VSP.

The improved technique can be employed for any number of VSPs at the first data storage system, for effecting failover of each VSP to the second data storage system, or to a respective other data storage system, in accordance with the particular VSP-specific settings of each VSP. Where the first data storage system serves all data objects available to hosts using VSPs, complete failover can be effected of the entire first data storage system to the second data storage system (or to respective other data storage systems). The technique can be applied for any number of data storage systems, with such systems forming a metro-cluster, where interrupted operation of one data storage system (or any VSP thereof) is seamlessly restored on another data storage system with little or no disruption to hosts.

The improved technique thus significantly reduces the administrative burdens of configuring replication and failover on individual data objects. By operating on data objects through their VSPs, the improved technique simplifies failover operations, which promotes both administrative convenience and data availability.

In accordance with improvements hereof, certain embodiments are directed to a method of managing failover of VSPs (Virtualized Storage Processors) from a first data storage system to a second data storage system. The method includes establishing synchronous replication settings for each of a set of VSPs in the first data storage system on a per-VSP basis. The method further includes operating the set of VSPs in the first data storage system. Each of the set of VSPs includes multiple data objects, where each data object is any of a file system, a LUN (logical storage unit), and a vVOL (virtual volume). The method further includes receiving IO requests at the first data storage system designating data to be written to data objects of the set of VSPs operating in the first data storage system and synchronously replicating the IO requests received at the first data storage system to the second data storage system in accordance with the synchronous replication settings for each respective one of the set of VSPs to create a passive replica of each of the set of VSPs at the second data storage system. The method still further includes, in response to a failure of the first data storage system, activating the replica of each of the set of VSPs at the second data storage system to provide active operation of the set of VSPs at the second data storage system.

Other embodiments are directed to a data storage apparatus constructed and arranged to perform the method described above. Still other embodiments are directed to a computer program product. The computer program product stores instructions, which when executed on one or more processing units of a data storage apparatus, cause the data storage apparatus to perform the method described above. Some embodiments involve activity that is performed at a single location, while other embodiments involve activity that is distributed over a computerized environment (e.g., over a network).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other features and advantages will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. In the accompanying drawings,

FIG. 1 is a block diagram showing an example environment in which improved techniques hereof may be practiced, wherein the example environment includes a data storage system having a storage processor;

FIG. 2 is a block diagram showing an example IO stack of the storage processor shown in of FIG. 1;

FIG. 3 is a block diagram showing example features of the IO stack of FIG. 2 in additional detail;

FIG. 4 is a block diagram showing synchronous replication between a first data storage system at a first site and a second data storage system at a second site;

FIG. 5 is an example screen generated by a graphical user interface (GUI) application for establishing replication settings of data objects on a per-user-object basis;

FIG. 6 is another example screen generated by the GUI application for establishing synchronous replication settings on a per-data-object basis;

FIG. 7 is another example screen generated by the GUI application for establishing asynchronous replication settings on a per-user-object basis;

FIG. 8 is a block diagram showing an example technique for asynchronously replicating a LUN by consuming snaps;

FIG. 9 is a block diagram showing an example technique for asynchronously replicating a host file system by consuming snaps;

FIG. 10 is a block diagram showing an example technique for asynchronously replicating a data object using a replication splitter and replication appliance;

FIG. 11 is a block diagram showing example records of a configuration database that associates VSPs with data objects;

FIG. 12 is a block diagram of an IO stack of the data storage system of FIG. 1, which associates data objects of particular VSPs with respective consistency groups; and

FIG. 13 is a block diagram showing synchronous replication of VSPs between a first data storage system at a first site and a second data storage system at a second site;

FIG. 14 is a block diagram showing failover operations on the second data storage system at a second site following a failure at the first data storage system at the first site; and

FIG. 15 is a flowchart showing an example method for managing failover of VSPs from a first data storage system to a second data storage system.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described. It is understood that such embodiments are provided by way of example to illustrate various features and principles of the invention, and that the invention hereof is broader than the specific example embodiments disclosed.

An improved technique for managing failover from a first data storage system to a second data storage system includes configuring replication settings for data objects associated with VSPs on a per-VSP basis, such that all of the data objects associated with each VSP share common replication settings. As the first data storage system operates a VSP, replication operations on the first data storage system replicate data written to any of the data objects of the VSP to the second data storage system, in accordance with the VSP-specific replication settings for the VSP, such that the second data storage system acquires and stores a passive replica of the VSP. In the event of a failure at the first data storage system, operations fail over the entire VSP, including all of its data objects, to the second data storage system, and activate the passive replica of the VSP at the second data storage system to restore host access to the data objects of the VSP.

This document is presented in sections to assist the reader in identifying desired information. In the material that follows:

-   -   Section I presents an example environment in which improved         techniques hereof may be practiced and describes, inter alia, a         unified datapath architecture for expressing both block-based         objects and file-based objects as respective underlying volumes         and underlying files, which enables the use of a common         replication approach for both block-based and file-based         objects.     -   Section II presents particular example improvements for         effecting synchronous replication of both block-based and         file-based objects on a per-user-object basis under the         direction of a common replication session manager.     -   Section III presents particular improvements for unifying both         synchronous and asynchronous replication of both block-based and         file-based objects.     -   Section IV presents particular improvements for extending         synchronous replication on a per-user-object basis to VSPs         (Virtualized Storage Processors), where each VSP is treated as a         data object and replication on VSPs is conducted on a per-VSP         basis.     -   Section V presents particular improvements for extending         VSP-based synchronous replication to a metro-cluster-type         arrangement where a VSP is synchronously replicated from a first         site to a second site and a failure at the first site causes the         VSP to failover to the second site and resume operation at the         second site.         I) Example Environment Including Unified Datapath Architecture:

FIG. 1 shows an example environment 100 in which embodiments of the improved technique hereof can be practiced. Here, multiple host computing devices (“hosts”), shown as devices 110(1) through 110(N), access a data storage system 116 over a network 114. The data storage system 116 includes a storage processor, or “SP,” 120 and storage 180. The storage 180 is provided, for example, in the form of hard disk drives and/or electronic flash drives. The data storage system 116 may include multiple SPs like the SP 120 (see, for example, a second SP 120 a). For instance, multiple SPs may be provided as circuit board assemblies, or “blades,” which plug into a chassis that encloses and cools the SPs. The chassis has a backplane for interconnecting the SPs, and additional connections may be made among SPs using cables. It is understood, however, that no particular hardware configuration is required, as any number of SPs (including a single one) can be provided and the SP 120 can be any type of computing device capable of processing host IOs.

The network 114 can be any type of network or combination of networks, such as a storage area network (SAN), local area network (LAN), wide area network (WAN), the Internet, and/or some other type of network, for example. In an example, the hosts 110(1-N) connect to the SP 120 using various technologies. For example, the host 110(1) can connect to the SP 120 using Fibre Channel (e.g., through a SAN). The hosts 110(2-N) can connect to the SP 120 using TCP/IP, to support, for example, iSCSI, NFS, SMB 3.0, and CIFS. Any number of hosts 110(1-N) may be provided, using any of the above protocols, some subset thereof, or other protocols besides those shown. As is known, Fibre Channel and iSCSI are block-based protocols, whereas NFS, SMB 3.0, and CIFS are file-based protocols. The SP 120 is configured to receive IO requests 112(1-N) according to both block-based and file-based protocols and to respond to such IO requests 112(1-N) by reading or writing the storage 180.

The SP 120 is seen to include one or more communication interfaces 122, a set of processing units 124, and memory 130. The communication interfaces 122 include, for example, adapters, such as SCSI target adapters and network interface adapters, for converting electronic and/or optical signals received from the network 114 to electronic form for use by the SP 120. The set of processing units 124 include one or more processing chips and/or assemblies. In a particular example, the set of processing units 124 includes numerous multi-core CPUs. The memory 130 includes both volatile memory (e.g., RAM), and non-volatile memory, such as one or more ROMs, disk drives, solid state drives (SSDs), and the like. The set of processing units 124 and the memory 130 together form control circuitry, which is constructed and arranged to carry out various methods and functions as described herein. Also, the memory 130 includes a variety of software constructs realized in the form of executable instructions. When the executable instructions are run by the set of processing units 124, the set of processing units 124 are caused to carry out the operations of the software constructs. Although certain software constructs are specifically shown and described, it is understood that the memory 130 typically includes many other software constructs, which are not shown, such as various applications, processes, and daemons.

As shown, the memory 130 includes an operating system 134, such as Unix, Linux, or Windows™, for example. The memory 130 further includes a container 132. In an example, the container 132 is a software process that provides an isolated userspace execution context within the operating system 134. In various examples, the memory 130 may include multiple containers like the container 132, with each container providing its own isolated userspace instance. Although containers provide isolated environments that do not directly interact (and thus promote fault containment), different containers can run on the same kernel (not shown) and can communicate with one another using inter-process communication (IPC) mediated by the kernel. Containers are well-known features of Unix, Linux, and other operating systems.

In the example of FIG. 1, only a single container 132 is shown. Running within the container 132 is an IO stack 140, a replication session manager 162, a Graphical User Interface (GUI)-based application 164, and multiple VSPs (Virtualized Storage Processors) VSP 1 to VSP N. A VSP is a collection of data objects, internal file systems, and servers (e.g., NFS and/or CIFS servers), which together provide a mechanism for grouping objects and providing a common set of network interfaces such that the VSP appears from outside the SP 120 as similar to a physical SP. More information about VSPs may be found in copending U.S. patent application Ser. No. 13/828,294, filed Mar. 14, 2013, the contents and teachings of which are hereby incorporated by reference in their entirety. Although certain components are shown residing within the container 132, alternatively different components reside in different containers. For example, the GUI-application 164 may run within a dedicated container and communicate with the replication session manager 162 using IPC.

The IO stack 140 provides an execution path for host IOs (e.g., IO requests 112(1-N)) and includes a front end 142 and a back end 144. In alternative arrangements, the back end 144 is located on another SP (e.g., SP 120 a) or is provided in a block-based array connected to the SP 120 (e.g., in a gateway configuration).

The replication appliance 160 assists in performing block-based replication of both block-based objects and file-based objects to a second data storage system, which may be located locally to the data storage system 116 or remotely. In an example, the replication appliance 160 takes the form of a hardware unit, and multiple such units may be provided, e.g., for supporting strong data compression and other advanced features. For purposes of this document, it is understood that this document refers to the replication appliance 160 as a single component, although that component include any number of units, which operate in coordination with one another, e.g., in a cluster.

The replication session manager 162 controls the establishment of replication settings on particular data objects, including VSPs. The replication session manager 162 establishes replication settings on a per-data-object basis, conducts replication sessions with replica sites, and orchestrates replication activities, including recovery and failover activities.

The GUI application 164 provides a user interface for configuring the replication session manager 162, e.g., for establishing replication settings on particular data objects. As the IO stack 140, replication appliance 160 (optionally), replication session manager 162, and GUI application 164 all run within the same container 132, the IO stack 140, replication appliance 160 (optionally), and replication session manager 162 can communicate with one another using APIs (application program interfaces) and pointer passing and without the need to use IPC.

The memory 130 is further seen to include a configuration database 170. The configuration database 170 stores configuration information pertaining to the data storage system 116, including information about the VSPs 1-N and the data objects with which they are associated. In other implementations, the data storage system 116 stores the configuration database 170 elsewhere, such as or in the storage 180, on a disk drive of flash drive separate from the SP 120 but accessible to the SP 120, e.g., over a backplane or network, or in some other location.

In operation, the hosts 110(1-N) issue IO requests 112(1-N) to the data storage apparatus 116. The IO requests 112(1-N) may include both block-based requests and file-based requests. The SP 120 receives the IO requests 112(1-N) at the communication interfaces 122 and passes the IO requests to the IO stack 140 for further processing. At the front end 142, processing may include mapping IO requests directed to LUNs, host file systems, vVOLs (virtual volumes, e.g., as soon available for VMware, Inc. of Palo Alto, Calif.), VMDKs (virtual memory disks), and other data objects to block-based requests presented to internal volumes, as well as mapping the internal volumes to respective files stored in a set of internal file systems of the data storage system 116. Host IO requests received at the SP 120 for reading and writing block-based objects and file-based objects are thus converted to reads and writes of respective volumes, which are then converted to reads and writes of respective files. As will be described further below, the front end 142 may perform block-based synchronous replication at the level of the internal volumes, where the front end 142 presents both block-based objects and file-based objects in block-based form. After processing by the front end 142, the IO requests propagate to the back end 144, where the back end 144 executes commands for reading and/or writing the physical storage 180, agnostically to whether the data read and/or written is directed to a block-based object or a file-based object.

FIG. 2 shows the front end 142 and back end 144 of the IO stack 140 in additional detail. Here, the front end 142 is seen to include protocol end points 220, a data object layer 222, an object-volume mapping layer 224, a replication splitter 226, a volume-file mapping 228, lower-deck (internal) file systems 230, a storage pool 232, and a basic volume interface 236. The back end 144 is seen to include a host side adapter 250, a RAID (Redundant Array of Independent Disks) manager 252, and hard disk drive/electronic flash drive support 254. Although IO requests 112 enter the IO stack 140 from the top and propagate down (from the perspective of FIG. 2), for ease of understanding, the different components of the IO stack 140 are described herein from the bottom up.

At the back end 144, the hard disk drive/electronic flash drive support 254 includes drivers that perform the actual reading from and writing to the storage 180. The RAID manager 252 accesses particular storage units (slices) written or read using RAID protocols. The host side adapter 250 provides an interface to the front end 142, for instances in which the front end 142 and back end 144 are run on different machines. When the front end 142 and back end 144 are co-located on the same SP, as they are in FIG. 1, the host side adapter 250 may be omitted or made to perform no operation.

Continuing to the front end 142, the basic volume interface 236 provides an interface to the back end 144 for instances in which the front end 142 and back end 144 are run on different hardware, The basic volume interface 236 may also be inactive in the arrangement shown in FIG. 1.

The storage pool 232 organizes elements of the storage 180 in the form of slices. A “slice” is an increment of storage space, such as 256 MB or 1 GB in size, which is derived from the storage 180. The pool 232 may allocate slices to lower-deck file systems 230 for use in storing their files. The pool 232 may also deallocate slices from lower-deck file systems 230 if the storage provided by the slices is no longer required. In an example, the storage pool 232 creates slices by accessing RAID groups formed by the RAID manager 252, dividing the RAID groups into FLUs (Flare LUNs), and further dividing the FLU's into slices.

The lower-deck file systems 230 are built upon slices managed by a storage pool 232 and represent both block-based objects and file-based objects internally in the form of files. The data storage system 116 may host any number of lower-deck file systems 230, and each lower-deck file system may include any number of files. In a typical arrangement, a different lower-deck file system is provided for each data object to be stored. Each lower-deck file system includes one file that stores the data object itself and, in some instances includes other files that store snaps of the file that stores the data object. Each lower-deck file system 230 has an inode table. The inode table provides a different inode for each file stored in the respective lower-deck file system. The inode table may also store properties of the file(s), such as their ownership and block locations at which the file's/files' data are stored.

The volume-file mapping 228 maps each file representing a data object to a respective volume, which is accessible using block-based semantics. The volume-file mapping can be achieved in a variety of ways. According to one example, a file representing a data object is regarded as a range of blocks (e.g., 8K allocation units), and the range of blocks can be expressed as a corresponding range of offsets into the file. Because volumes are accessed based on starting location (logical unit number) and offsets in the volume, the volume-file mapping 228 can establish a one-to-one correspondence between offsets into the file and offsets into the corresponding internal volume, thereby providing the requisite mapping needed to express the file in the form of a volume.

The replication splitter 226 sits above the volume-file mapping 228. The replication splitter 226 is configurable by the replication session manager 162 on a per-data-object basis to intercept IO requests and to replicate the data specified to be written in such requests according to data-object-specific settings. Depending on the data object to which the IO request is directed and the replication settings defined for that object, the replication splitter 226 may allow IO requests it receives to pass through to the volume-file mapping 228 unimpeded (e.g., if no replication is specified for that data object). Alternatively, the replication splitter 226 may intercept the IO request, forward the request to the replication appliance 160, and hold the request until the replication splitter 226 receives an acknowledgement back from the replication appliance 160. Once the acknowledgement is received, the replication splitter 226 may allow the IO request to continue propagating down the IO stack 140. It should be understood that the replication session manager 162 can configure the replications splitter 226 in a variety of ways for responding to different types of IO requests. For example, replication session manager 162 can configure the replication splitter 226 to operate in a pass-through mode for control IOs and for IO requests specifying data reads. In some situations, the replication session manager 162 can configure the replication splitter 226 to intercept reads as well as writes. In any such situations, the replication session manager 162 can configure the replication splitter 226 on a per-data-object basis.

The object-volume mapping layer 224 maps internal volumes to respective data objects, such as LUNs, host file systems, and vVOLs. Mapping underlying volumes to host-accessible LUNs may simply involve a remapping operation from a format compatible with the internal volume to a format compatible with the LUN. Mapping internal volumes to host file systems, however, may be accomplished in part by leveraging from the fact that file systems are customarily built upon volumes, such that an underlying volume is part of the structure of a host file system. Host file systems, also called “upper-deck file systems,” are thus built upon the internal volumes presented by the volume-file mapping 228 to provide hosts with access to files and directories. Mapping of vVOLs can be achieved in similar ways. For block-based vVOLs, the object-volume mapping layer 224 may perform mapping substantially as it does for LUNs. File-based vVOLs may be mapped, for example, by converting host-specified offsets into vVOL files to corresponding offsets into internal volumes.

The protocol end points 220 expose the underlying data objects to hosts in accordance with respective protocols for accessing the data objects. Thus, the protocol end points 220 may expose block-based objects (e.g., LUNs and block-based vVOLs) using Fiber Channel or iSCSI and may expose file-based objects (e.g., host file systems, file-based vVOLs, and VMDKs) using NFS, CIFS, or SMB 3.0, for example.

In operation, the IO stack 140 receives an IO request 112 specifying data to be written to a particular data object. The object-volume mapping 224 maps the IO request 112 to a block-based request 112 a directed to an internal volume. The replication splitter 226 may intercept the block-based request 112 a and send the block-based request 112 a to the replication appliance 160 (or may pass through the IO request, depending on settings established by the replication session manager 162 for the data object). Assuming the replication splitter 226 intercepts the block-based request 112 a, the replication appliance 160 coordinates with other components to replicate the data specified in the block-based request 112 a at a second site and provides the replication splitter 226 with an acknowledgement. When the replication splitter 226 receives the acknowledgement, the replication splitter 226 allows the block-based request 112 a to continue propagating down the IO stack 140. The volume-file mapping 228 maps the block-based request 112 a to one that is directed to a particular file of a lower-deck file system, and the back end 144 and storage 180 process the IO request by writing the specified data to actual media. In this manner, the IO stack 140 supports both local storage of the data specified in the IO request 112 and replication at a second site.

FIG. 3 shows portions of the front end 142 in additional detail. Here, data objects include a LUN 310 and an HFS (host file system) 312. The object-volume mapping 224 includes a LUN-to-Volume mapping 320 and an HFS-to-Volume mapping 322. Using the approach described above, the LUN-to-Volume mapping 320 maps the LUN 310 to a first volume 324, and the HFS-to-Volume mapping 322 maps the HFS 312 to a second volume 326. The replication splitter 226 may intercept IOs in accordance with settings established by the replication session manager 262 (as described above). The Volume-to-File mapping 228 maps the first and second internal volumes 324 and 328 to respective files 336 (F1) and 346 (F2) in respective lower-deck files systems 330 and 340. Through the various mappings, any set of blocks of the LUN 310 specified in an IO request 112 is mapped to a corresponding set of blocks within the first file 336. Similarly, any file or directory of the HFS 312 specified in an IO request 112 is mapped to a corresponding set of blocks within the second file 346.

The lower-deck file system 330 includes an inode table 332, and the lower-deck file system 340 includes an inode table 342. An inode 334 provides file-specific information about the first file 336, and an inode 344 provides file-specific information about the second file 346. The information stored in each inode includes location information (e.g., block locations) where data of the respective file are stored.

Although a single file is shown for each of the lower-deck file systems 330 and 340, it is understood that each of the lower-deck file systems 330 and 340 may include any number of files, with each having its own entry in the respective inode table. In one example, each lower-deck file system stores not only the file F1 or F2, but also snaps of those files, and therefore snaps of the data objects the files store. For example, the first lower-deck file system 330 stores the first file 336 representing the LUN 310 along with a different file for each snap of the LUN 310. Similarly, the second lower-deck file system 340 stores the second file 346 representing the HFS 312 along with a different file for every snap of the HFS 312.

As shown, the storage pool 232 allocates slices 360 for providing storage for the first file 336 and the second file 346. In the example show, slices S1 through S4 store the data of the first file 336, and slices S5 through S7 store the data of the second file 346. The data that make up the LUN 310 are thus stored in the slices S1 through S4, whereas the data that make up the HFS 312 are stored in the slices S5 through S7.

II) Synchronous Replication of Block-Based and File-Based Objects:

Example techniques for performing synchronous replication on both block-based objects and file-based objects are now described in connection with FIGS. 4-7. As is known, “synchronous” replication refers to replication performed in band with IO requests 112 as the IO requests arrive. With synchronous replication, individual IO request data are generally persisted to a replica site on an individual basis, e.g., one-by-one, as the IO requests arrive. In contrast, “asynchronous” replication is performed out of band with individual IO requests, with replicas generated, for example, on demand, at regular intervals, and/or in response to particular events.

FIG. 4 shows an example arrangement for performing synchronous replication of a data object 412 from a first data storage system 116 (as shown in FIG. 1) to a second data storage system 416. Here, the first data storage system 116 is located at a first site 410 and the second data storage system 416 is located at a second site 420. In an example, the first site 410 and the second site 420 are located at different geographical locations, such as in different buildings of a city or campus. The second data storage system 416 includes persistent storage 480 (e.g., disk drives, flash drives, and the like) and is operatively connected to a second replication appliance 460. The second replication appliance 460 includes a buffer 462, which may be implemented in non-volatile memory (e.g., on disk or flash). In some examples, the buffer 462 is implemented in high-speed non-volatile memory within the storage 480, but separate and apart from any replica storage. Further, the second replication appliance 460 may be included entirely within the second data storage 116, similar to the way in which the first replication appliance 160 is included within the first data storage system 116 (see FIG. 1). Although the components at the first site 410 and the second site 420 are shown to be different, they may alternatively be the same, so as to provide symmetrical behavior, with each site storing a replica of data objects from the other. As shown in this example, however, the first site 410 acts to receive and process IO requests 112 from hosts, whereas the second site 420 acts to provide a replica 422 of the data object 412 on the first site 410.

The encircled numbers in FIG. 4 identify an example sequence of events. At (1), the first data storage system 116 receives an IO request 112 specifying data to be written in the storage 180 for a particular data object 412 (e.g., a LUN, a host file system, a vVOL, etc.). The IO request 112 propagates down the IO stack 140 (FIG. 2) and encounters the replication splitter 226. The replication splitter 226 intercepts the IO request and temporarily prevents the IO request from propagating further down the IO stack 140 (FIG. 2). At (2), the replication splitter 226 sends the IO request (e.g., a version thereof) to the first replication appliance 160. At (3), the first replication appliance 160 forwards the IO request to the second replication appliance 460, which stores the data specified in the IO request in the buffer 462. At (4), the second replication appliance 460 acknowledges safe storage of the IO data to the first replication appliance 160 (e.g., that the IO data are persisted in the buffer 462). At (5), the first replication appliance 160 in turn acknowledges receipt to the replication splitter 226. Only when the replication splitter 226 receives the acknowledgement does the replication splitter 226 allow the IO request to continue propagating down the IO stack 140 (FIG. 2) to complete the write operation to the storage 180. At (6), the first data storage system 116 acknowledges completion of the IO request 112 back to the originating host. Asynchronously with the IO request, the second replication appliance 460 may de-stage the buffer 462 to the replica 422 of the data object maintained in the storage 480. For example, at (7), the data specified in the IO request are transferred from the buffer 462 to the storage 480, and at (8), the second data storage system acknowledges completion.

Many variants are contemplated. For example, the buffer 462 may be realized using volatile memory (e.g., RAM). In such cases, the second replication appliance 460 may wait to acknowledge a write to the first replication appliance 160 until it receives confirmation that the data specified in the IO request has been persisted in the replica 422 for the data object 412 in the storage 480.

As described, the first data storage system 116 conducts synchronous replication with the second data storage system 416 on a per-data-object basis and in accordance with object-specific settings. The replication session manager 162 establishes these settings and orchestrates replication activities, recovery activities, and failover activities. In an example, the GUI application 164 provides an entry point to the replication session manger 162 to allow users to specify object-specific settings. In some examples, the GUI application is configured to accept user input for managing a wide range of operations of the data storage system 116, including configuring pools, configuring block-based objects, and configuring file-based objects, as well as for managing replication. Although particular aspects of the GUI application 164 are described herein in relation to replication, it is understood that the GUI application 164 may have a much greater scope than for controlling replication alone. For example, in some implementations, the GUI application 164 is a modified form of the Unisphere integrated management tool, available from EMC Corporation of Hopkinton, Mass. Providing the GUI application 164 within Unisphere simplifies the user experience by avoiding for the user to operate a separate GUI for controlling replication.

FIG. 5 shows an example screen shot 500 of the GUI application 164 that allows users to specify object-specific replication settings. It is understood that the screen 500 is shown in simplified form and is intended to be merely illustrative. Here, the screen 500 includes a control 510 for selecting a desired data object. In an example, a user clicks the control 510 to reveal a list of available objects. The control 510 may organize the data objects in multiple levels, e.g., in a first level 520 that lists different types of data object (e.g., LUNs, Host File Systems, etc.) and in a second level 530 that lists particular data objects of a type the user selects from the first level 520 (e.g., LUN 1, LUN 2, etc.). In an example, the GUI application 164 queries the configuration database 170 and/or other databases to obtain lists of available data objects and stores such lists in connection with the control 510. A user may click the control 510 to display a list of object types objects in the first level 520. The user may then and click a desired type from the list displayed at first level 520 to cause the control 510 to display a list of data objects of the selected type in the second level 530. A different list is displayed in the second level 530 for each selection in the first level 520. The user may then click a particular listed data object to establish configuration settings for that object. For example, the user may click “LUNs” from the first level 520 and then click “LUN 2” from the second level 530 to configure settings for LUN 2.

The user may next click a control 550 to select a particular data protection operation. List 560 appears when the user clicks the control 550 and displays example options. These include, for example, “Synch Replication” for synchronous replication and “Async Replication” for asynchronous replication. The user may the click a button 580 (“SETUP”) to configure settings for the selected replication type (selected via control 550) on the selected data object (selected via control 510).

FIG. 6 shows an example screen 600 of the GUI application 164, which the GUI application displays, for example, when the user selects “LUN 2” with the control 510 and selects “Sync Replication” from the control 550 (FIG. 5). The GUI application 164 thus accepts user input, via the screen 600, for establishing synchronous replication settings specific to LUN 2. It is understood that the screen 600 can be configured to accept settings for different data objects when the user selects them, e.g., using the control 510. Also, different screens may be displayed when the user selects different replication types (e.g., using the control 550).

The screen 600 accepts a number of different replication settings. These include, for example, the following settings:

-   -   Replication Appliance Address (610): The address (e.g., SCSI or         IP address) of the replication appliance 160. Different         replication appliance addresses may be provided for different         data objects. For example, multiple replication appliances (like         the appliance 160) may be connected to the data storage system         116 over a SAN (storage area network) or other network.         Assigning different replication appliance addresses to different         data objects causes different replication appliances to be used         for replicating the respective objects. In some examples,         replication appliances are arranged into clusters. In such         cases, the Replication Appliance Address 610 may designate a         cluster address. Where a cluster address is specified, the         replication splitter 226 may select individual appliance units         within a cluster based on load, for example.     -   Replication Site Address (612): The address (e.g., IP address)         of a data storage system or a replication appliance at a second         site. In the example of FIG. 4, the replication site address can         be the address of the second replication appliance 460 or the         address of an SP running on the second data storage system 416.     -   Max Remote Buffer Size (614): The maximum amount of data that         may be stored in a buffer at the second site. In the example of         FIG. 4, the Max Remote Buffer Size refers to the amount of data         in the buffer 462 from IO requests 112 that have not yet been         committed to the replica 422 in the storage 480. By setting Max         Remote Buffer Size 614 to a large value, a considerable amount         of time may be required to de-stage data to the replica 422 in         the storage 480 to bring the replica 422 up to date with the         data object at the first site 410. By setting Max Remote Buffer         Size 614 to a small value, little time is needed to commit         pending data, such that the replica 422 is kept nearly up to         date with the original object at all times.     -   Max RTO (616): The maximum amount of time (Recovery Time         Objective) that the data object may remain unavailable to hosts         after the data object becomes unavailable at its source. In the         example of FIG. 4, the Max RTO 616 is the maximum amount of time         that is allowed to pass after a failure at the source before the         replica of the data object in the storage 480 is brought up to         date with the source and made available to hosts. In general,         the more uncommitted IO requests that are pending in the buffer         462, the greater amount of time required to activate the         replica. Therefore, an effective way to reduce RTO is set the         Max Remote Buffer Size 614 to a small value. As Max RTO 616 is         closely related to Max Remote Buffer Size 614, some         implementations may not offer the option to control both.         The example settings 610, 612, 614, and 616 are shown for         illustrative purposes. It is understood, however, that the         particular settings shown are not necessarily required nor are         they intended to represent all possible settings that may be         desired.

The screen 600 is further seen to include buttons 618 and 620, for establishing failover settings and recovery settings, respectively, for the selected data object. In an example, clicking the button 618 brings up a failover screen (not shown) for accepting user input to establish failover settings for the data object. Failover settings may include, for example, an address of a failover site, a maximum allowable amount of data loss (RPO), a maximum RTO, as above, as well as other settings. Clicking the button 620 may bring up a recovery screen (not shown) for accepting user input to establish recovery settings for the selected data object. Recovery settings may include, for example, a recovery destination (e.g., a location to which a replica is to be restored), as well as maximum RPO and RTO settings to be applied for recovery operations.

Although the screens 500 and 600 have been shown and described in connection with a particular data object (LUN 2), it should be understood that similar screens may be presented for other LUNs, and for other types of data objects, with the screens 500 and 600 accepting user settings for any currently selected object. Thus, the GUI application 164 may be used for establishing replication, failover, and recovery settings on a per-data-object basis, with each data object having its own respective settings.

As further shown in FIG. 6, the GUI application 164 may generate output providing sync replication settings for the selected object. For example, the GUI application 164 may gather all user-established settings specified in the screens 500 and 600 (as well as any settings gathered from the failover screen and/or recovery screen) and provide such object-specific settings in an output file 630(1). Additional output files (e.g., 630(2), 630(3), . . . ) may be provided for other data objects, e.g., one per data object. It should be readily apparent, however, that object-specific settings may be stored in any suitable way, such as in different files (as shown), as a single file (e.g., an XML file), as records in a database, or in any number of other ways. In any case, the GUI application 164 sends the object-specific settings to the replication session manager 162, which receives the settings and applies them to establish replication sessions with replica sites for each data object in accordance with its respective settings. In this manner, the GUI application 164 may act as a single entry point to the replication session manager 162 for controlling replication on a per-object basis.

The replication session manager 162 may orchestrate any number of replication sessions at any given time, with each replication session operating to replicate a respective data object. For each replication session, the replication session manager 162 communicates with a respective replica site (e.g., with a counterpart replication session manager at the replica site) and coordinates replication activities in accordance with the object-specific settings. In the event of a failure at the data storage system 116 that renders a data object or the entire data storage system 116 unavailable, the replication session manager at the replica site can orchestrate failover and/or recovery operations in accordance with the same settings established in the replication session manager 162 on the data storage system 116.

As further shown in FIG. 6, the replication session manager 162 may also receive information describing file system restrictions. These restrictions may apply to upper-deck file systems. They may also apply to lower-deck file systems, i.e., to the file systems in which the file realizations of the data objects themselves are stored (FIGS. 2 and 3). Any of such file systems may operate subject to restrictions, such as restrictions prohibiting deletion prior to a certain date. These restrictions may include File Level Retention for compliance (FLR-C) and/or File Level Retention for enterprises (FLR-E). When restriction information is provided for a particular data object, the replication session manager 162 receives the information and includes it with the object-specific settings for the data object. When replication is conducted on the object, the replica site obtains the restriction information and applies the identified restrictions to the replica. The replica is thus made subject to the same restrictions as the original object.

Although the GUI application 164 accepts user input for establishing various replication settings for a data object, the replication session manager 162 may, in some examples, generate synchronous replication settings for a data object on its own, automatically, and without user input, and initiate a replication session for the data object with a destination object in accordance with the automatically generated settings. Thus, replication may proceed on a data object even if a user does nothing to establish replication settings.

Once the replication session manager 162 receives object-specific replication settings for a particular data object, the replication session manager 162 configures the replication splitter 226 (FIGS. 2-4) to operate in accordance with the settings for the respective object. In an example, the replication session manager 162 identifies a particular internal volume (FIGS. 2 and 3) in the IO stack 140 that the object-volume mapping 224 maps to the data object. The replication session manager 162 then activates the replication splitter 226 on the identified volume. Then, whenever the replication splitter 226 receives an IO request specifying data to be written to the internal volume mapped to the data object, the replication splitter 226 performs replication activities in accordance with the settings for the data object. These include, for example, sending the IO request to the replication appliance 160 designated in the settings for the object, configuring the buffer (e.g., 462), and so forth. Because the replication splitter 226 recognizes volumes and because the replication session manager 262 can identify the internal volume for each data object, the replication splitter 226 and the replication manager 260 can together manage replication on a per-data-object basis.

The above-described technique performs synchronous replication on both block-based objects and file-based objects. The technique may be used in connection with a data storage system 116 that internally stores data objects (e.g., LUNs, file systems, block-based vVOLs, file-based vVOLs, VMDKs, etc.) in the form of respective files (e.g., files 336, 346), such that each file provides a realization of a data object. The data storage system 116 maps each such file to a respective logical volume (e.g., 324, 326), and each logical volume provides a block-based interface. As the data storage system receives IO requests 112 (e.g., from hosts 110(1) to 110(N)) specifying data to be written to a data object, the data storage system 116 renders the IO requests as block-based requests, regardless of whether the IO requests are themselves block-based or file-based. A block-based replication splitter intercepts the block-based requests directed to the logical volumes and performs block-based, synchronous replication on the block-based requests, thereby achieving synchronous replication of both block-based objects and file-based objects in a single, unified architecture. The technique typically results in a reduced need for multiple, diverse replication solutions, and thus fewer items that must be purchased, learned, and maintained.

III) Synchronous and Asynchronous Replication of Block-Based and File-Based Objects:

Example techniques for performing asynchronous replication for both block-based objects and file-based objects are now described in connection with FIGS. 7-11. It is understood that the asynchronous replication techniques described in this section may be used independently of the synchronous techniques described in Section II above or may be used alongside such synchronous replication techniques. For example, the replication session manager 162 may establish settings for both synchronous and asynchronous replication for any given data object (LUN, file system, vVOL, etc.) and may conduct a synchronous replication session and an asynchronous replication session on the same data object or on different objects at the same time or at different times. For example, at the same time that synchronous replication proceeds on a data object in band with IO requests directed to the data object, asynchronous replication may also proceed, out of band with IO requests but on some timing schedule (hourly, daily, etc.) or in response to various events. It is understood that the asynchronous replication techniques described herein may be conducted in the same or a similar environment to that disclosed in Section I, i.e., in the same environment where the above-disclosed synchronous replication technique is performed.

As it does with synchronous replication, the replication session manager 162 establishes settings for performing asynchronous replication, orchestrates asynchronous replication sessions with replica sites, and orchestrates recovery and/or failover operations, all on a per-data-object basis. The same GUI application 164 accepts user input for configuring both synchronous and asynchronous settings and thus provides an entry point to the replication session manager 162 with respect to both synchronous and asynchronous replication.

FIG. 7 shows an example screen 700 generated by the GUI application 164 for configuring asynchronous replication settings for data objects on a per-data-object basis. The GUI application 164 generates the screen 700, for example, when the user selects “LUN 2” with the control 510 and “Async Replication” with the control 550 (FIG. 5). The screen 700 thus collects user input for establishing asynchronous replication settings specific to LUN 2. The screen 700 is shown in simplified form and is intended to be merely illustrative.

Screen 700 accepts user input for a variety of settings, some of which may be similar to those presented in the screen 600. For example, the screen 700 accepts a setting 712 for Replication Site Address, which is similar to the setting 612 but specifies a site address for asynchronous replication. This site address may be the same as that specified for synchronous replication or it may be different. The screen 700 also presents buttons 718 and 720, which perform similar functions to those performed by the buttons 618 and 620, i.e., to establish failover settings and recovery settings, respectively. In some implementations, the screen 700 also accepts a setting 710, similar to the setting 610, for a Replication Appliance Address, which may be the same or different from any Replication Appliance Address 610 specified for synchronous replication. Although replication appliances have been described above in connection with synchronous replication, certain embodiments hereof also employ replication appliances for performing asynchronous replication. The screen 700 may also accept a setting 714 that allows a user to provide a desired Async Replication Frequency 714, i.e., how often to perform asynchronous replication operations. Example entries for setting 714 may include “Hourly,” “Daily,” and so on. The screen 700 may accept additional asynchronous settings (not shown), such as for designating events that trigger asynchronous replication activities.

Although the screen 700 has been shown and described in connection with a particular data object (LUN 2), it should be understood that similar screens may be presented for other LUNs, and for other types of data objects, with the screen accepting user settings for any currently selected object. Also, the example settings 710, 712, and 714 are shown for illustrative purposes. It is understood that the particular settings shown are not necessarily required nor are they intended to represent all possible settings that may be desired.

The screen 700 generates output that provides asynchronous replication settings for the selected object. For example, the GUI application 164 may gather all user-established settings specified in the screen 700 (as well as any settings gathered from the failover screen and/or recovery screen) and provide such object-specific settings in an output file 730(1). Additional output files (e.g., 730(2), 730(3), . . . ) may be provided for additional data objects, e.g., one per data object. However, object-specific settings may be stored in any suitable way, such as in different files (as shown), as a single file (e.g., an XML file), as records in a database, or in any number of other ways. Also, such records or files may be combined with those (e.g., 630(1), 630(2), . . . )) for storing synchronous replication settings in a single location or set of locations.

The GUI application 164 sends the object-specific settings to the replication session manager 162, which receives the settings and may apply them to establish asynchronous replication sessions with specified replica sites for each data object in accordance with its respective settings.

The replication session manager 162 may orchestrate any number of asynchronous replication sessions at any given time, with each asynchronous replication session operating to replicate a respective data object. Also, the replication session manager 162 may operate multiple asynchronous replication sessions on any data object simultaneously (e.g., for replicating the same object to different sites). For each asynchronous replication session, the replication session manager 162 communicates with a respective replica site (e.g., with a counterpart replication session manager at the replica site) and coordinates replication activities in accordance with the object-specific settings. In the event of a failure at the data storage system 116 that renders a data object or the entire data storage system 116 unavailable, the replication session manager at the replica site can orchestrate failover and/or recovery operations in accordance with the same settings established in the replication session manager 162 on the data storage system 116.

The replication session manager 162 may apply the information describing file system restrictions in a manner similar to that described above for synchronous replication. When the replication session manager 162 conducts asynchronous replication on a particular data object stored in a file system to which file system restrictions apply, the replication session manager 162 communicates the restriction information to the replica site, e.g., in the async replication settings for the object. The replica site then applies the identified restrictions to the replica. The replica is thus made to be subject to the same restrictions as the original object. Thus, restrictions are passed from the source to the replica for asynchronous replication in a manner similar to that described above for synchronous replication.

In a manner similar to that described above for synchronous replication, the replication session manager 162 may, in some examples, generate asynchronous replication settings for a data object on its own, automatically, and without user input, and initiate an asynchronous replication session for the data object with a destination object in accordance with the automatically generated settings. Thus, asynchronous replication may proceed on a data object even if a user does nothing to establish asynchronous replication settings.

The data storage system 116 may employ various techniques for effecting asynchronous replication. One technique operates by consuming snaps of the underlying files that realize the data objects. Another technique employs the replication splitter 226.

FIG. 8 shows an example technique for effecting asynchronous replication of a LUN using snaps. Here, the replication session manager 162 has snapped the file 336 that realizes the LUN 310 (F1 from FIG. 3) to create a first snap 336(1) (F1-1) of the LUN 310 and a second snap 336(2) (F1-2) of the LUN 310. Like the LUN 310 itself, the snaps 336(1) and 336(2) are stored as files in the lower-deck file system 330. Also, in the same way that the file 336 has an inode 334 in the inode table 332 of the lower-deck file system 330, so too do the files 336(1) and 336(2) have inodes 334(1) and 334(2), respectively in the inode table 332.

On some predetermined schedule and/or in response to events as defined in the data-object-specific settings for the LUN 310, the replication session manager 162 creates new snaps of the LUN 310. Each time a new snap is taken, a new file 336(i) is created and a new inode 334(i) is allocated from the inode table 332. In an example, all snaps of the LUN 310 are stored in the lower-deck file system 330.

In the manner described above, the session manager 162 computes a difference between the two most recent snaps (here, 336(1) and 336(2)) and sends the difference to an asynchronous replication site, again as specified in the data-object-specific settings for the LUN 310. More generally, each time a new snap 336(i) is created, the asynchronous replication manager 1130 computes a new difference based on the most recent snap 336(i) and the immediately preceding snap 336(i−1) and sends the new difference to the asynchronous replication site.

The asynchronous replication technique shown in FIG. 8 is based on snapping files, regardless of the content of those files. Thus, although FIG. 8 shows an example of asynchronous replication of the LUN 310, it is understood that the same technique can be generalized to other data objects that are similarly represented as files in lower-deck file systems. Thus, the asynchronous replication technique of FIG. 8 can be used for asynchronously replicating not only LUNs, but also file systems, block-based vVOLs, file-based vVOLs, and other data objects.

For example, FIG. 9 shows an example technique for effecting asynchronous replication of an HFS using snaps. Here, the replication session manager 162 has snapped the file 346 that realizes the HFS 312 (F2 from FIG. 3) to create a first snap 346(1) (F2-1) of the HFS 312 and a second snap 346(2) (F2-2) of the HFS 312. Like the HFS 312 itself, the snaps 346(1) and 346(2) are stored as files in the lower-deck file system 340. Also, in the same way that the file 346 has an inode 344 in the inode table 342 of the lower-deck file system 340, so too do the files 346(1) and 346(2) have inodes 344(1) and 344(2), respectively in the inode table 342.

On some predetermined schedule and/or in response to events as defined in the data-object-specific settings for the HFS 312, the replication session manager 162 creates new snaps of the HFS 312. Each time a new snap is taken, a new file 346(i) is created and a new inode 344(i) is allocated from the inode table 342. In an example, all snaps of the HFS 312 are stored in the lower-deck file system 340.

The replication session manager 162 takes snaps of the HFS 312, computes a difference between snaps, and sends the difference to an asynchronous replication site, as specified in the data-object-specific settings for the HFS 312 and in a manner similar to that described for the LUN 310.

FIG. 10 shows an example technique for effecting asynchronous replication of a data object using the replication splitter 226. Here, the replication session manager 162 configures the replication splitter 226 (FIGS. 2-4) to operate in accordance with the data-object-specific settings for performing asynchronous replication on the data object. In an example, the replication session manager 162 identifies the internal volume (FIGS. 2 and 3) corresponding to the data object in the IO stack 140 and activates the replication splitter 226 on the identified volume. Then, whenever the replication splitter 226 receives an IO request specifying data to be written to the internal volume, the replication splitter 226 performs actions in accordance with the object-specific asynchronous settings for the data object. These settings may differ from those specified for synchronous replication, or in some circumstances may be the same.

In an example, the replication session manager 162 directs the replication splitter 226, in accordance with the object-specific settings, to intercept IO requests specifying writes to an object and to prevent them from propagating further down the IO stack 140 (FIG. 2) until the replication splitter 226 receives acknowledgements from the first replication appliance 160 (i.e., in a manner similar to actions performed for synchronous replication). In this case, however, the first replication appliance 160 has been configured in accordance to the object-specific settings to provide acknowledgements as soon as it persists the specified data locally, e.g., in the appliance 160 itself. The first replication appliance 160 accumulates data from the replication splitter 226 and sends them to the second site 420 on a regular basis and/or upon the occurrence of specified events, i.e., in accordance with the data-object-specific settings for the object.

The encircled numbers in FIG. 10 show an example sequence for performing asynchronous replication. At (1′), the first data storage system 116 receives an IO request 112 from a host (e.g., one of 110(1-N)). The IO request 112 specifies data to be written to a particular data object, e.g., the data object 412 in the storage 180. The IO request 112 propagates down the IO stack 140 (FIG. 2) and reaches the replication splitter 226.

At (2′), the replication splitter 226, acting in accordance with the object-specific asynchronous replication settings for the object 412, mirrors the IO request 112 (i.e., a block-based form thereof) to the first replication appliance 160. The replication splitter 226 also prevents the IO request from propagating further down the IO stack 140.

At (3′), the first replication appliance 160 sends an acknowledgement to the replication splitter 226, confirming that it has received and persisted the data specified in the IO request. In response to receiving the acknowledgement, the replication splitter 226 allows the IO request to continue propagating down the IO stack 140 to effect writing of the data specified in the IO request 112 to the storage 180.

At (4′), the first data storage system 116 sends an acknowledgement back to the host that originated the IO request 112, confirming that the IO request 112 has been processed.

At (5′), which may occur at some later time after the first replication appliance 160 has accumulated data from multiple IO requests, the first replication appliance 160 sends the accumulated data to the second replication appliance 460 at the second site 420. the second replication appliance 460 stores the data in the buffer 462.

At (6′), the second replication appliance 160 sends the data to the second data storage system 416, which writes the data to a replica 1022. The replica 1022 is a replica of the object 422 generated via asynchronous replication and thus may differ from the replica 422 (FIG. 4) generated by synchronous replication.

At (7′), the data storage system 416 acknowledges to the second replication appliance 460 that the replica 1022 has been written, and at (8′), the second replication appliance 460 sends an acknowledgement back to the first replication appliance 160.

The above sequence can be repeated on a regular basis and/or in response to particular events, as specified in the data-object-specific settings, to ensure that the state of the replica 1022 does not fall far behind that of the object 412. Of course, the above sequence may also be used for asynchronously replicating other data objects.

Many variants of this asynchronous replication sequence are contemplated. According to one variant, the replication session manager 162 may direct the replication splitter 226 in accordance with data-object-specific settings to mirror IO requests specifying writes to the first replication appliance 160 (or to some other appliance) without holding back the IO requests until acknowledgements are received. Thus, the first data storage system 116 may process IO requests in the usual way, with the replication splitter 226 operating to mirror IO requests but not to intercept them.

The above-described technique manages synchronous replication and asynchronous replication of both block-based objects and file-based objects via a common replication session manager 162 configured from a common GUI application 164. The replication session manager 162 can access different settings for different data objects (e.g., LUNs, file systems, block-based vVOLs (virtual volumes), file-based vVOLs, VMDKs, etc.), with replication settings maintained on a per-data-object basis. The replication session manager can also orchestrate synchronous and/or asynchronous replication sessions, failover, and/or recovery, for any given data object in accordance with the particular settings established for that object.

IV) Synchronous Replication of Virtualized Storage Processors (VSPs):

Example techniques for performing synchronous replication of VSPs are now described in connection with FIGS. 11-13. It is understood that the techniques disclosed in this section are consistent with those described in Section II above for synchronous replication of data objects and may be performed in the same or a similar environment to that disclosed in Section I, i.e., in the same environment where the above-disclosed synchronous replication techniques are performed.

FIG. 11 shows an example set of records 1100 of the configuration database 170 (FIG. 1), which provide definitions for VSPs 1-N. For each VSP, a record specifies an owning SP, authentication information, and identifiers of data objects (e.g., file systems) associated with the respective VSP, including identifiers of internal file systems (e.g., a root file system and a configuration file system) and various user file systems or other data objects. The record may further specify various host interfaces that define host IO protocols that the respective VSP is equipped to handle. The record for each VSP thus identifies not only data objects associated with the VSP, but also a set of interfaces and settings that form a “personality.” This personality enables the VSP to interact with hosts in a manner similar to the way a physical storage processor interacts with hosts.

In operation, VSPs are instantiated on the owning SP by starting their respective host interfaces. The interfaces for each VSP can respond to host IO requests for reading and writing the data objects of the respective VSP, which are stored in the storage 180.

Referring briefly back to FIG. 5, which shows a screen 500 displayed by the GUI application 164, it is seen that one of the types of objects that a user may select for configuring replication via the control 510 are “VSPs.” For example, a user may click “VSPs” at the first level 520 for control 510, in response to which the control 510 displays a list of available VSPs in the second level 530, similar to the manner in which a list of LUNs is displayed in the example of FIG. 5. The user may then click a particular VSP, e.g., “VSP 1,” to select VSP 1 as the object on which to configure replication. The user may then operate the control 520 to select “Sync Replication” and click the “SETUP” button 580. In response, the GUI application 164 displays a screen like the screen 600 of FIG. 6, but which is tailored to VSP 1. The user may then establish VSP-specific synchronous replication settings for VSP 1, by providing input to the controls 610, 612, 614, and 616, for example. The user may also click the buttons 618 and 620 to establish failover settings and recovery settings, respectively, for VSP 1, e.g., in a manner similar to that described for “LUN 2” in connection with FIG. 5 in Section II above.

The GUI application 164 may store settings for VSP 1 in a file 630(1) or in some other data structure. Settings for other VSPs may be stored in other files or structures (e.g., 630(2), 630(3), . . . ), i.e., on a per-VSP basis.

The GUI application 164 sends the VSP-specific settings (e.g., the file 630(1) for VSP 1) to the replication session manager 162, which receives the settings and applies them to establish replication sessions for each data object associated with the VSP in accordance with the VSP-specific settings. For example, the replication session manager 162 queries the configuration database 170 to obtain the record for VSP 1, which provides a list of all of the data objects associated with VSP 1. The replication session manager 162 then initiates a synchronous replication session for each of the data objects specified in the record, with the replication session for each data object conducted in accordance with the settings established for VSP 1. For operational reasons and in some examples, the replication session manager may exclude the root file system for a VSP from replication, i.e., no replication session is conducted for the root file system. Rather, a new root file system containing site-specific information may be constructed for a VSP at the replica site. Similar operations may be repeated for other VSPs, e.g., for VSP 2, VSP 3, etc., using the VSP-specific settings for those VSPs.

The replication session manager 162 thus handles the complexity of establishing settings for large numbers of individual data objects by receiving one set of settings for a VSP and applying the settings across all of the data objects associated with the VSP. If a VSP is associated with 100 different data objects, synchronous replication for all 100 objects can be handled by establishing one set of settings. The administrative burden of managing replication for large numbers of data objects is thus greatly reduced.

The replication session manager 162 may orchestrate any number of replication sessions for a VSP, or for multiple VSPs, at any given time, with each replication session operating to replicate a respective set of data objects. For each replication session operated for a VSP, the replication session manager 162 communicates with a replica site (e.g., with a counterpart replication session manager at the replica site) and coordinates replication activities in accordance with the VSP-specific settings. In the event of a failure at the data storage system 116 that renders the VSP or the entire data storage system 116 unavailable, the replication session manager at the replica site can orchestrate failover and/or recovery operations on each data object associated with the VSP in accordance with the same VSP-specific settings established in the replication session manager 162 on the data storage system 116.

As the replication session manager 162 conducts replication sessions for a VSP, the replication session manager 162 can receive information describing file system restrictions that apply to individual data objects associated with the VSP on a per-data-object basis and provide such information to the replica site. The replica site then applies the identified restrictions to the replica. The replica for each data object of a VSP is thus made subject to the same restrictions as the original object.

Although the GUI application 164 accepts user input for establishing various replication settings for a VSP, the replication session manager 162 may, in some examples, generate synchronous replication settings for a VSP on its own, automatically, and without user input, and initiate a replication session on each data object of the VSP with a respective destination object in accordance with the automatically generated, VSP-specific settings. Thus, replication may proceed for a VSP even if a user does nothing to establish replication settings.

Once the replication session manager 162 receives synchronous replication settings for a particular VSP, the replication session manager 162 configures the replication splitter 226 (FIGS. 2-4) to operate in accordance with the settings for that VSP. In an example, the replication session manager 162 identifies an internal volume (FIGS. 2 and 3) in the IO stack 140 that the object-volume mapping 224 maps to each data object associated with the VSP. The replication session manager 162 then activates the replication splitter 226 on the identified volumes. Then, whenever the replication splitter 226 receives an IO request specifying data to be written to any of the internal volumes mapped to the data objects of the VSP, the replication splitter 226 performs replication activities in accordance with the VSP-specific settings. These include, for example, sending the IO request to the replication appliance 160 designated in the VSP-specific settings, configuring the buffer (e.g., 462), and so forth. Because the replication splitter 226 recognizes volumes and because the replication session manager 262 can identify the internal volumes for all of the data objects of a VSP, the replication splitter 226 and the replication manager 260 can together manage replication on a per-VSP basis. This operation can be more fully understood with reference to FIG. 12.

FIG. 12 shows a view of the IO stack 140 in which VSPs are associated with consistency groups. The mapping shown in FIG. 12 of lower-deck files to data objects is similar to that shown in FIGS. 2 and 3, except that FIG. 12 shows data objects organized in VSPs and logical volumes organized in consistency groups. Here, the volume-file mapping 228 maps lower-deck files FA, FB, and FC to respective logical volumes HFS A Vol, HFS B Vol, and HFS C Vol. The volume-file mapping 228 also maps lower-deck files FD, FE, and FF to respective logical volumes HFS D Vol, HFS E Vol, and HFS F Vol. The object-volume mapping 224 then maps logical volumes HFS A Vol through HFS F Vol to respective host (upper-deck) file systems HFS A through HFS F. In this example, the host file systems HFS A, HFS B, and HFS C belong to a first VSP (VSP 1), and the host file systems HFS D, HFS E, and HFS F belong to a second VSP (VSP 2).

Once the replication session manager 162 has received VSP-specific replication settings for VSP 1, the replication session manager 162 identifies each data object associated with VSP 1 (e.g., by accessing the records 1100 for VSP 1). The replication session manager 162 also identifies the logical volume that corresponds to each data object associated with VSP 1. In an example, the replication session manager 162 obtains logical volume identities from a driver that manages the IO stack 140 or a portion thereof. The replication session manager 162 may perform similar activities for VSP 2.

In an example, the replication session manager 162 directs the replication splitter 226 to form a first consistency group CG 1 from the logical volumes that correspond to the data objects of VSP 1, i.e., HFS A Vol, HFS B Vol, and HFS C Vol. Similarly, the replication session manager 162 directs the replication splitter 226 to form a second consistency group CG 2 from the logical volumes that correspond to the data objects of VSP 2, i.e., HFS D Vol, HFS E Vol, and HFS F Vol. The replication session manager 162 then activates the replication splitter 226 to perform synchronous replication operations on a per-consistency-group basis. In particular, the replication session manager 162 activates the replication splitter 226 to operate in accordance with a first set of synchronous replication settings for logical volumes belonging to CG 1 and to operate in accordance with a second set of synchronous replication settings for logical volumes belonging to CG 2, where the first set of synchronous replication settings are those specified for VSP 1 and the second set of replication settings are those specified for VSP 2. Since the volumes of CG 1 correspond to the data objects of VSP 1 and the volumes of CG 2 correspond to the data objects of VSP 2, the replication splitter 226 is made to operate on a per-VSP basis. Thus, as IO requests are received specifying data to be written to any data object of VSP 1, the replication splitter performs synchronous replication actions in accordance with the VSP-specific settings for VSP 1. Similarly, as IO requests are received specifying data to be written to any data object of VSP 2, the replication splitter performs synchronous replication actions in accordance with the VSP-specific settings for VSP 2.

With the replication splitter 226 configured according to VSP-specific settings, synchronous replication of data objects proceeds substantially as described in connection with FIG. 4 in Section II above, i.e., by rendering each IO request 112 as a block-based request, mirroring the block-based request to a replication appliance, and preventing the request from propagating further down the IO stack 140 until the replication appliance acknowledges that the data specified in the block-based request have been persisted at the remote site.

The above-described technique for managing replication of VSPs (Virtualized Storage Processors) proceeds on a per-VSP basis by (i) identifying the data objects associated with a VSP, (ii) establishing a common set of replication settings across all of the data objects associated with the VSP, and (iii) replicating the VSP by replicating each of the identified data objects associated with the VSP in accordance with the common set of replication settings established across all of the data objects associated with the VSP. The improved technique avoids the need for administrators to separately configure and manage replication on large numbers of individual data objects and thus reduces administrative burdens.

V) Metro-Cluster Based on VSP Synchronous Replication:

Example techniques for performing failover of VSPs and/or entire sites are now described in connection with FIGS. 13-15. It is understood that the techniques described in this section may build upon those described in the preceding sections and may be performed in the same or a similar environment to those described in Section I and may be used with the same types of replication as those described in Sections II, III, and IV above.

Through the use of synchronous replication of VSPs as described in Section IV, it is possible to achieve failover of VSPs, and even of entire data storage systems, with operation restored at failover sites in mere seconds or less. Multiple data storage systems can thus be arranged in a metro-cluster, with active sites in the metro-cluster failing over their VSPs to passive sites and with passive sites activating the VSPs to restore access to hosts.

FIGS. 13 and 14 show an example arrangement for conducting failover of VSPs from the first site 410 (FIG. 4) to the second site 420. In FIG. 13, it is seen that multiple VSPs (VSP 1 to VSP N) operate on the first data storage system 116. For example, the data storage system 116 runs servers and interfaces of the VSPs 1-N and the data storage system 116 and receives and processes IO requests 112 directed to data objects associated with the VSPs 1-N.

Taking VSP 1 as an example, IO requests 112 specifying data to be written to any of the data objects of VSP 1 arrive at the first data storage system 116, and the replication splitter 226 mirrors the requests to the second site 210 in accordance with the VSP-specific replications settings for VSP 1, e.g., in the manner described for synchronous replication of VSPs in Section IV. In the event of a failure at the first data storage system 116, operations for VSP 1 fail over to the second data storage system 416.

An example sequence is shown by the encircled numbers in FIG. 13. At (1″), an IO request 112 arrives. The IO request 112 specifies data to be written to one of the data objects 1312 associated with VSP 1. The IO request 112 propagates down the IO stack 140 (FIGS. 2, 3, and 12). The object-volume mapping 224 maps the IO request 112 to a block-based request 112 a (FIG. 2) directed to a logical volume. The replication splitter 226 recognizes the logical volume as belonging to a particular consistency group (e.g., CG 1, FIG. 12), and applies synchronous replication settings specific to CG 1. The replication splitter 226 has received these settings from the replication session manager 162 (FIG. 6), which in turn has received the settings from the GUI application 164 (i.e., the settings entered for VSP 1). In accordance with these settings, the replication splitter 226 temporarily prevents the block-based request 112 a from propagating further down the IO stack 140 and, at (2″), mirrors the block-based request to the first replication appliance 160.

At (3″), the first replication appliance 160 forwards the data specified in the block-based request 112 a to the second replication appliance 460. The second replication appliance 460 receives the data and stores the data persistently in the buffer 462.

At (4″), the second replication appliance 460 acknowledges persistent storage of the data back to the first replication appliance 160, and at (5″), the first replication appliance 160 sends an acknowledgement back to the replication splitter 226.

The replication splitter receives the acknowledgement from (5″) and releases the block-based request 112 a, so that it may resume propagating down the IO stack 140. The first data storage system 116 processes the block-based request 112 a and persistently stores the specified data in the storage 180, i.e., in the portion of the storage 180 storing data objects 1312 associated with VSP 1.

At (6″), the first data storage system 116 sends an acknowledgement back to the originating host (which originated the IO request 112), confirming that the IO request 112 has been successfully processed.

At (7″), the second replication appliance 460 de-stages the received data from the buffer 462 to the second data storage system 416, i.e., to a replica 1322 of VSP 1 in the storage 480. The data in the replica 1322 is thus made to maintain a passive replica of VSP 1 (shown also as VSP 1R) at the second data storage system 416.

At (8″), the second data storage system 416 acknowledges back to the second replication appliance 460, and synchronous replication of the IO request 112 is complete.

It is understood that actions at (7″) and (8″) need not be performed synchronously; rather, de-staging the buffer 462 may occur with less strict timing requirements than persisting the data at (4″), because once the data for the IO request are persisted in the buffer 462, the data may be considered as safely received.

Although the example above applies to one IO request 112 for one data object of one VSP (VSP 1), it is evident that essentially the same acts can be performed for other IO requests, other data objects, and other VSPs, to maintain respective replicas VSP 1R to VSP NR at the second data storage system 416. Synchronous replication of IO requests directed to VSPs 1 to VSP N on the first data storage system 116 to replicas VSP 1R to VSP NR on the second data storage system 416 can thus proceed over time to reflect changes in the underlying data objects.

FIG. 14 shows the same arrangement as in FIG. 13, but depicts circumstances following a site failure at the first site 410. In an example, the second site 420 detects an outage at the first site 410. The second site 420 may detect the outage by being directly informed (e.g., via a message from the first site 410 over a network) that the first site 410 is down. In some cases, the first site 410 may be completely unable to contact the second site. However, in an example, the first replication appliance 160 and the second replication appliance 460 maintain near constant communication, e.g., via heartbeat signals, a watchdog or arbitrator at a third site, or other means, such that the second replication appliance 460 can detect an outage at the first site 410 soon after it occurs, even if the first site 410 is unable to send any message.

Once the second site 420 detects the outage at the first site 410, the second site 420 takes action to restore operation of VSP 1 to VSP N from the second site 410. However, due to the asynchronous de-staging of IO request data from the buffer 462 to the storage 480 (described in connection with acts 7″ and 8″ above), the replicas of VSPs 1R to NR in the storage 480 at the second site 420 may not be current with the VSPs 1 to N at the first site 410. Thus, the failover operations at the second site include completing the de-staging of any IO request data for VSPs received from the first site 210 to the storage 480.

Once all the IO data for a particular VSP have been transferred from the buffer 462 to the storage 480, the second data storage system 416 activates the respective VSP replica to bring the VSP replica online. The second data storage system 416 may start the servers and interfaces for the VSP replica (the settings for which are obtained, for example, from the VSP replica's configuration database—see FIG. 11) and begin processing IO requests 112 directed to data objects of the VSP replica from hosts. The VSP replica then becomes the active version of the VSP, with the original VSP on the failed site falling behind. The same acts may be repeated for each of the other VSPs, by making their respective replicas current and starting their servers and interfaces.

Although the first site 410 and second site 420 are shown asymmetrically, with the site 410 acting as a source and the site 420 acting as a destination, alternatively the first site 410 and the second site 420 are constructed symmetrically, such that each receives IO requests and uses VSP-based synchronous replication for mirroring its own VSPs to the other. Further, although only two data storage systems 116 and 416 are shown, any number of data storage systems may be operated together, e.g., in a metro-cluster. Each data storage system may conduct VSP-based synchronous replication with any number of other data storage systems in the cluster, with failover coordinated among cluster members.

A number of variants of the above sequence have been contemplated. For example, the second site 420 may apply a higher priority to restoring some VSPs than it applies for restoring others. In an example, the GUI application 164 (FIGS. 5 and 6) presents a priority failover setting, which may be accessed on the screen presented when the user clicks the “Failover Settings” button 618. The screen may accept choices such as “High,” “Medium,” and “Low,” for establishing failover priority of the VSP. The GUI application 164 stores the priority settings in the VSP-specific files or data structures (e.g., 630(1, 2, . . . )). The replication session manager 162 receives the VSP-specific priority settings and communicates the priority settings within the session that it establishes with the second site 420.

Also, it has been described that bringing a VSP online at the second site 420 involves de-staging the data for that VSP stored in the buffer 462 to the storage 480. Thus, the minimum time required to restore operation of a VSP at the second site 420 may be limited by the amount of data stored for the VSP in the buffer 462. Administrators may thus wish to provide settings for Max Remote Buffer Size 614 and/or “Max RTO” 616 (FIG. 6) when establishing VSP-specific settings for VSPs using the GUI application 164. In an example, the second replication appliance 460 enforces the Max Remote Buffer Size 614 and/or the Max RTO 616 settings for a particular VSP through a process called “regulation,” whereby the second replication appliance 460 delays sending acknowledgments back to the first replication appliance 160 (e.g., at act 4″ of FIG. 13) to prevent the contents of the buffer 462 from growing too large or too quickly. Such regulation can be applied both to maintain a specified maximum buffer size and to maintain a specified maximum RTO.

Further, failover is described in the example above as applying to an entire site. However, failover may alternatively be limited to a particular VSP or to a particular set of VSPs.

FIG. 15 shows an example process 1500 for managing failover of VSPs (Virtualized Storage Processors) from a first data storage system to a second data storage system. The method 1500 may be carried out, for example, in connection with the data storage apparatus 116, such as by the software constructs described in connection with FIGS. 1-3, which reside in the memory 130 of the storage processor 120 and are run by the set of processing units 124. The various acts of the method 1500 may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in orders different from those illustrated, which may include performing some acts simultaneously, even though the acts are shown as sequential in the illustrated embodiments.

At step 1510, synchronous replication settings are established for each of a set of VSPs in the first data storage system on a per-VSP basis. For example, the GUI application 164 may receive user input for establishing synchronous replication settings on a per-VSP basis, described in Section IV and shown in FIGS. 5 and 6.

At step 1512, the set of VSPs are operated in the first data storage system. Each of the set of VSPs includes multiple data objects, where each data object is any of a file system, a LUN (logical storage unit), and a vVOL (virtual volume). For example, as shown in FIG. 13, VSPs 1-N are operated in the first data storage system 116. Each VSP includes multiple data objects, shown by way of example as objects 1312 of VSP 1.

At step 1514, IO requests are received at the first data storage system designating data to be written to data objects of the set of VSPs operating in the first data storage system. For example, the first data storage system 116 receives IO requests 112.

At step 1516, the IO requests received at the first data storage system are synchronously replicated to the second data storage system in accordance with the synchronous replication settings for each respective one of the set of VSPs to create a passive replica of each of the set of VSPs at the second data storage system. For example, FIGS. 10 and 13 show VSP synchronous replication and FIG. 13 shows the creation of passive replicas VSP 1R to VSP NR.

At 1518 and in response to a failure of the first data storage system, the replica of each of the set of VSPs is activated at the second data storage system to provide active operation of the set of VSPs at the second data storage system. For example, as shown in FIG. 14, the VSP replicas VSP 1R to VSP NR are activated to restore operation of the VSPs on the second data storage system.

An improved technique has been described for managing failover from a first data storage system to a second data storage system. The technique includes configuring replication settings for data objects associated with VSPs on a per-VSP basis, such that all of the data objects associated with each VSP share common replication settings. As the first data storage system operates a VSP, replication operations on the first data storage system replicate data written to any of the data objects of the VSP to the second data storage system, in accordance with the VSP-specific replication settings for the VSP, such that the second data storage system acquires and stores a passive replica of the VSP. In the event of a failure at the first data storage system, operations fail over the entire VSP, including all of its data objects, to the second data storage system, and activate the passive replica of the VSP at the second data storage system to restore host access to the data objects of the VSP.

The improved technique can be employed for any number of VSPs at the first data storage system, for effecting failover of each VSP to the second data storage system, or to a respective other data storage system, in accordance with the particular VSP-specific settings of each VSP. Where the first data storage system serves all data objects available to hosts using VSPs, complete failover can be effected of the entire first data storage system to the second data storage system (or to respective other data storage systems). Thus, data storage systems can be made to operate in a metro-cluster, where interrupted operation of one data storage system (or any VSP thereof) is seamlessly restored on another data storage system with little or no disruption to hosts.

The improved technique thus significantly reduces the administrative burdens of configuring replication and failover on individual data objects. By operating on data objects through their VSPs, the improved technique simplifies failover operations, which promotes both administrative convenience and data availability.

As used throughout this document, the words “comprising,” “including,” and “having” are intended to set forth certain items, steps, elements, or aspects of something in an open-ended fashion. Although certain embodiments are disclosed herein, it is understood that these are provided by way of example only and the invention is not limited to these particular embodiments. In addition, the word “set” as used herein indicates one or more of something, unless a statement is made to the contrary.

Having described certain embodiments, numerous alternative embodiments or variations can be made. For example, the improvements or portions thereof may be embodied as a non-transient computer-readable storage medium, such as a magnetic disk, magnetic tape, compact disk, DVD, optical disk, flash memory, Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA), and the like (shown by way of example as medium 1150 in FIG. 15). Multiple computer-readable media may be used. The medium (or media) may be encoded with instructions which, when executed on one or more computers or other processors, perform methods that implement the various processes described herein. Such medium (or media) may be considered an article of manufacture or a machine, and may be transportable from one machine to another.

Further, although features are shown and described with reference to particular embodiments hereof, such features may be included in any of the disclosed embodiments and their variants. Thus, it is understood that features disclosed in connection with any embodiment can be included as variants of any other embodiment, whether such inclusion is made explicit herein or not.

Those skilled in the art will therefore understand that various changes in form and detail may be made to the embodiments disclosed herein without departing from the scope of the invention. 

What is claimed is:
 1. A method of managing failover of VSPs (Virtualized Storage Processors) from a first data storage system to a second data storage system, comprising: establishing synchronous replication settings for each of a set of VSPs in the first data storage system on a per-VSP basis; operating the set of VSPs in the first data storage system, each of the set of VSPs including multiple data objects, each data object being any of a file system, a LUN (logical storage unit), and a vVOL (virtual volume); receiving IO requests at the first data storage system designating data to be written to data objects of the set of VSPs operating in the first data storage system; synchronously replicating the IO requests received at the first data storage system to the second data storage system in accordance with the synchronous replication settings for each respective one of the set of VSPs to create a passive replica of each of the set of VSPs at the second data storage system; and in response to a failure of the first data storage system, activating the replica of each of the set of VSPs at the second data storage system to provide active operation of the set of VSPs at the second data storage system, wherein, when receiving the IO requests, each of the set of VSPs (i) includes a respective grouping of data objects and a respective set of host interfaces and (ii) is operated on a physical storage processor in the first data storage system, wherein each of the set of VSPs interacts with multiple host computing devices via the set of host interfaces to process IO requests received from the host computing devices, and wherein activating the replica includes starting the set of host interfaces of each of the set of VSPs on a physical storage processor in the second data storage system to enable each VSP to process IO requests from the host computing device directed to the respective data objects.
 2. The method of claim 1, wherein synchronously replicating the IO requests received at the first data storage system includes, for each IO request, (i) sending the IO request to a replication appliance, (ii) storing the data specified to be written by the IO request in a buffer in the replication appliance, (iii) sending an acknowledgement back to the first data storage system confirming that the data specified in the IO request have been stored in the buffer, and (iv) writing the data specified in the IO request to the second data storage system.
 3. The method of claim 2, further comprising, in response to the failure of the first data storage system and prior to activating the replica of each of the set of VSPs on the second data storage system, writing the data stored in the buffer of the replication appliance and not already written to the second data storage system to the second data storage system.
 4. The method of claim 3, further comprising establishing failover settings for each of the set of VSPs on a per-VSP basis.
 5. The method of claim 4, further comprising specifying a maximum amount of data that may be stored in the buffer in the replication appliance.
 6. The method of claim 5, further comprising the replication appliance delaying sending acknowledgments back to the first data storage system to limit the amount of data stored in the buffer to within the specified maximum amount of data.
 7. The method of claim 4, further comprising specifying a maximum recovery time allowed between the failure on the first data storage system and a time when the replica of each of the set of VSPs on the second data storage system has been activated.
 8. The method of claim 7, further comprising the replication appliance delaying sending acknowledgments back to the first data storage system to limit the amount of data stored in the buffer and thereby to ensure that the second data storage system can meet the specified maximum recovery time.
 9. The method of claim 4, further comprising establishing different priorities for different VSPs of the set of VSPs, wherein activating the replica of each of the set of VSPs at the second data storage system includes activating VSPs of the set of VSPs having higher priority prior to activating VSPs of the set of VSPs having lower priority.
 10. A data storage system, comprising set of processors and memory, coupled to the set of processors, the set of processors together forming control circuitry constructed and arranged to: establish synchronous replication settings for each of a set of VSPs in a first data storage system on a per-VSP basis; operate the set of VSPs in the first data storage system, each of the set of VSPs including multiple data objects, each data object being any of a file system, a LUN (logical storage unit), and a vVOL (virtual volume); receive IO requests at the first data storage system designating data to be written to data objects of the set of VSPs operating in the first data storage system; synchronously replicate the IO requests received at the first data storage system to a second data storage system in accordance with the synchronous replication settings for each respective one of the set of VSPs to create a passive replica of each of the set of VSPs at the second data storage system; and in response to a failure of the first data storage system, activate the replica of each of the set of VSPs at the second data storage system to provide active operation of the set of VSPs at the second data storage system, wherein, with the control circuitry constructed and arranged to receive the IO requests, each of the set of VSPs (i) includes a respective grouping of data objects and a respective set of host interfaces and (ii) is constructed and arranged to operated on a physical storage processor in the first data storage system, wherein each of the set of VSPs is constructed and arranged to interact with multiple host computing devices via the set of host interfaces to process IO requests received from the host computing devices, and wherein the control circuitry, constructed and arranged to activate the replica, is further constructed and arranged to start a set of host interfaces of each of the set of VSPs on a storage processor in the second data storage system to enable each VSP to process IO requests from the host computing device directed to the respective data objects.
 11. The data storage system of claim 10, wherein the control circuitry to synchronously replicate the IO requests received at the first data storage system is further constructed and arranged to, for each IO request, (i) send the IO request to a replication appliance, (ii) store the data specified to be written by the IO request in a buffer in the replication appliance, (iii) send an acknowledgement back to the first data storage system confirming that the data specified in the IO request have been stored in the buffer, and (iv) write the data specified in the IO request to the second data storage system.
 12. The data storage system of claim 11, wherein the control circuitry is further constructed and arranged to, in response to the failure of the first data storage system and prior to activating the replica of each of the set of VSPs on the second data storage system, write the data stored in the buffer of the replication appliance and not already written to the second data storage system to the second data storage system.
 13. The data storage system of claim 12, wherein the control circuitry is further constructed and arranged to direct the replication appliance to delay sending acknowledgments back to the first data storage system to limit the amount of data stored in the buffer.
 14. A computer program product having at least one non-transitory computer-readable medium including instructions which, when executed by control circuitry, cause the control circuitry to perform a method of managing failover of VSPs (Virtualized Storage Processors) from a first data storage system to a second data storage system, the method comprising: establishing synchronous replication settings for each of a set of VSPs in the first data storage system on a per-VSP basis; operating the set of VSPs in the first data storage system, each of the set of VSPs including multiple data objects, each data object being any of a file system, a LUN (logical storage unit), and a vVOL (virtual volume); receiving IO requests at the first data storage system designating data to be written to data objects of the set of VSPs operating in the first data storage system; synchronously replicating the IO requests received at the first data storage system to the second data storage system in accordance with the synchronous replication settings for each respective one of the set of VSPs to create a passive replica of each of the set of VSPs at the second data storage system; and in response to a failure of the first data storage system, activating the replica of each of the set of VSPs at the second data storage system to provide active operation of the set of VSPs at the second data storage system, wherein, each of the set of VSPs operated on the first data storage system includes a respective grouping of data objects and a respective set of host interfaces, and wherein activating the replica includes starting a set of host interfaces of each of the set of VSPs on a storage processor in the second data storage system to enable each VSP to process IO requests from the host computing device directed to the respective data objects.
 15. The computer program product of claim 14, wherein synchronously replicating the IO requests received at the first data storage system includes, for each IO request, (i) sending the IO request to a replication appliance, (ii) storing the data specified to be written by the IO request in a buffer in the replication appliance, (iii) sending an acknowledgement back to the first data storage system confirming that the data specified in the IO request have been stored in the buffer, and (iv) writing the data specified in the IO request to the second data storage system.
 16. The computer program product of claim 15, wherein the method further comprises, in response to the failure of the first data storage system and prior to activating the replica of each of the set of VSPs on the second data storage system, writing the data stored in the buffer of the replication appliance and not already written to the second data storage system to the second data storage system.
 17. The computer program product of claim 16, wherein the method further comprises establishing failover settings for each of the set of VSPs on a per-VSP basis.
 18. The computer program product of claim 17, wherein the method further comprises specifying at least one of (i) a maximum amount of data that may be stored in the buffer in the replication appliance and (ii) a maximum recovery time allowed between the failure on the first data storage system and a time when the replica of each of the set of VSPs on the second data storage system has been activated.
 19. The computer program product of claim 18, wherein the method further comprises the replication appliance delaying sending acknowledgments back to the first data storage system to ensure that the set of VSPs can be activated quickly in the event of a failure of the first data storage system.
 20. The computer program product of claim 17, wherein the method further comprises establishing different priorities for different VSPs of the set of VSPs, wherein activating the replica of each of the set of VSPs at the second data storage system includes activating VSPs of the set of VSPs having higher priority prior to activating VSPs of the set of VSPs having lower priority. 